The MIMO (Multiple-Input Multiple-Output) system technology is a hot system technology to increase the utility efficiency of the spectrum with the minimum bandwidth in the wireless communication field. Signal detection of the receiving terminal is a critical task in an MIMO system. Accurate signal detection can effectively improve the error rate of bits in the system, reliability and frequency spectrum efficiency of the system also can be increased.
The ML (Maximum Likelihood) algorithm is the best signal-detection estimation method, wherein an exhaustive search method is used to compare the distances between all the possible signals sent out by the sending terminal and the signals received by the receiving terminal to find out a pair of signals having the shortest distance to the receiving terminal to be functioned as the final decision signal. However, the ML algorithm is too complicated to have rational computation cost and popular commercial application.
There have been many papers proposing algorithm to reduce the computational complexity of an MIMO system, including linear detection algorithm and nonlinear detection algorithm. However, the computational complexity is reduced but the error rate performance is suffered. In the linear detection algorithm, such as the ZF (zero forcing) algorithm and the MMSE (Minimum Mean Square Error) algorithm have lower computational complexity but higher performance loss. The nonlinear detection algorithm includes the V-BLAST (Vertical Bell Laboratories Layered Space Time) algorithm and the SD (Sphere Decoding) algorithm which has been introduced in many papers in recent years. The SD algorithm can achieve the performance of the ML algorithm and has been realized in many VLSI (Very Large Scale Integrated) circuits. However, the SD algorithm still has complexity higher than the V-BLAST algorithm.
Refer to Table. 1 to compare the complexity and performance of the conventional signal-detection algorithm. The algorithm having lower complexity usually has worse performance, and the algorithm having better performance usually has higher complexity.
TABLE 1The comparison sheet of the conventionalsignal-detection algorithmAlgorithmComplexityPerformanceZero Forcing algorithmlowworstMinimum Mean SquarelowgoodError algorithmVertical BelllowgoodLaboratories LayeredSpace Time algorithmMaximum LikelihoodhighbestalgorithmSphere Decodingvaries according tobestalgorithmsignal to noise ratio